Description of problem: xext.pc has "Requires.private: xau" so I think it should libXext-devel should require libXau-devel.
Actually, it should require libX11-devel (which will pull in libXau-devel).
* Tue Jan 31 2006 Mike A. Harris <mharris> 1.0.0-3 - Added "Requires: xorg-x11-proto-devel >= 7.0-1" to devel package (#173713) - Added "libX11-devel" to devel package (#176078)